1. Field of the Invention
The present invention relates to electrical cable enclosures and more particularly to telephone and electrical power cable enclosures for use in protecting utility cables in the above-ground transition between underground conduit and aerial transmission lines.
2. Description of the Prior Art
The term riser is used in the utility industry to refer to the section of electrical cable (telephone or power) that comes from underground conduit and extends up utility poles or buildings. In most locales, risers must be enclosed by means of conduit (pipe) or U-shaped enclosures usually to a height of 8 feet above ground level. Riser guards (also called cable guards) protect electrical cables from vandalism and rodent damage. In all cases, the material used for such riser guards is either polyvinyl chloride (PVC) plastic or metal (usually steel). The advantage of using a U-shaped guard as opposed to enclosed conduit is that access to the riser can be made by removing the U-shaped guard. From the standpoint of maintenance, this is an important feature. Conduit, because it totally encases the cable, restricts this access. For this reason, most telephone companies prefer the use of U-shaped guards. Whereas, power companies usually use conduit because power companies do not require access to the electrical cable as often as most telephone companies.
The performance requirements including crush and impact resistance and other standards for utility riser guards are specified by state Public Utilities Commissions (PUC's). Most PUC standards require that metal riser guards must be grounded to earth for basic safety reasons. Grounding of metal guards helps prevent an individual from being electrocuted by inadvertent contact with an electrically energized guard.
Some state PUC's have approved the use of an all dielectric U-shaped guard. Nonmetallic guards do not require grounding since dielectric materials do not conduct electricity. However, there are also very stringent electrical and mechanical requirements placed on the use of dielectric guards. For example, the California PUC stipulates that the crush and impact resistance of any U-shaped guard must be equal to or greater than two and one half (21/2) inch round schedule 80 PVC conduit as specified in the "National Electrical Manufacturers Association" (NEMA) Standards Publication No. TC 2-1978, paragraph TC 2-3.02 (crushing resistance) and TC 2-3.04 (impact resistance). There are no dielectric U-shaped guards on the market today that comply with the aforementioned NEMA standards. In most situations telephone companies need the flexibility provided by U-shaped riser guards, and therefore, telephone companies use the metallic U-shaped riser guards and suffer the inconvenience of grounding the enclosure.
Thus, what is desired is a dielectric U-shaped cable guard that will meet or exceed the stringent impact and crush resistance NEMA standards of the industry.
In addition, what is desired is a dielectric U-shaped cable guard that will closely interface with a variety of buried conduit sizes to keep water and foreign debris out of the buried cable conduit.